In a typical cellular radio system, wireless terminals, which are also known as mobile stations and/or user equipments (UEs), communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a NodeB, as in the case of an Universal Mobile Telecommunications System (UMTS) network, or an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node B (eNodeB,), as in the case of a Long Term Evolution (LTE) network. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations. In some radio access networks, several base stations are typically connected, e.g., by landlines or microwave, to a controller node, such as a Radio Network Controller (RNC) or a Base Station Controller (BSC), which supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks. LTE is a variant of a 3rd Generation Partnership Project (3GPP) radio access technology where the radio base station nodes are connected to a core network, via Access Gateways (AGWs), rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a RNC node are distributed between the radio base stations nodes, such as eNodeBs in LTE, and AGWs.
Discontinuous Reception (DRX) is used to save UE battery by providing a UE sleep-times where a UE does not need to monitor the downlink. However, for each DRX cycle, there is an active period during which the UE is active and monitors a number of downlink subframes such as Physical DownLink Control Channel (PDCCH) subframes as specified in 3GPP TS 36.321, Release 11, section 5.7.
Transmission and reception from a node, e.g., a radio terminal like a UE in a cellular system such as e.g. LTE, is multiplexed in the frequency domain or in the time domain, or combinations thereof. In Frequency Division Duplex (FDD), as illustrated to the left in FIG. 1, downlink and uplink transmission take place in different, sufficiently separated, frequency bands. In Time Division Duplex (TDD), as illustrated to the right in FIG. 1, downlink and uplink transmission take place in different, non-overlapping time slots. Thus, TDD operates in unpaired frequency spectrum, whereas FDD requires paired frequency spectrum.
TDD allows for different asymmetries in terms of the amount of resources allocated for uplink and downlink transmission, respectively, using different downlink/uplink configurations. In LTE, there are seven different configurations. Some TDD networks use a fixed frame configuration where some subframes are fixed as uplink and some are fixed as downlink. This prevents or at least limits the flexibility to adapt the uplink/downlink resource asymmetry to varying traffic situations. Recently, flexible subframes have been introduced so that three different types of subframes in a TDD system may be configured: a DownLink (DL) subframe, an UpLink (UL) subframe, and a “flexible” subframe. A frame structure may then include one or more downlink subframes preconfigured as a downlink subframe, one or more uplink subframes preconfigured as an uplink subframe, and one or more flexible subframes, where a flexible subframe is dynamically allocated to be an uplink subframe in one instance of a frame and a downlink subframe in another frame instance. This dynamic quality of the TDD frame is sometimes referred to as “dynamic TDD.”
For TDD with uplink and downlink subframe adaptation, i.e. dynamic TDD, a flexible subframe may be either uplink or downlink.